The present invention refers to a gear wheel, of the type having a profile capable of meshing with semi-encapsulation in a geared hydraulic apparatus.
Typical examples of geared hydraulic apparatus in which the gear wheels of the present invention, and to which specific reference shall be made hereinafter, find application are rotary positive displacement pumps, but the gear wheels of the present invention may also analogously be applied to hydraulic geared motors, which are thus deemed included within the scope of protection of the present invention. Rotary positive displacement pumps are generally made up of two gear wheels, in most cases of the straight cut gears, one of which, called driver, is connected to a driving shaft and rotates the other wheel, called driven.
A disadvantage particularly revealed by the abovementioned conventional gear pumps, generally with involute gear profile, lies in the fact that the pumped fluid is encapsulated, i.e. trapped, and compressed or however subjected to volume variations in the compartments enclosed between the gear profiles in the meshing area, thus leading to damaging and uncontrolled local stress peaks which are the source of direct operating noise.
Besides the direct operating noise indicated above, there is also a known problem arising from the phenomenon of irregularity, or “ripple”, in the transfer of the fluid which entails an indirect operating noise, known as ripple noise, linked to the flow rate pulsation and therefore pressure pulsation in the user circuit.
In other words, the oscillations in the fluid flow rate generate a pulsating wave which, via the fluid itself, is transmitted to the surrounding environment and, in particular, to the walls of the pump, to the piping and to the delivery pipes.
The induced noise may also reach unpredictable levels in the case where the aforesaid parts resonate with the oscillation or ripple frequency.